This invention relates generally to apparatus and methodology for effecting medical diagnosis and, more specifically, relates to systems and methodology utilizing ultrasonic techniques for such purposes.
Over the course of the last two to three decades, ultrasonic technology has played an ever-increasing role in medical diagnostics. Such techniques find applications in diagnosis of various medical aliments wherein it is useful to examine internal bodily organs with the objective of locating features or aspects of such organs which may be indicative of disease, abnormalities or so forth.
While early systems of the foregoing type included very limited capabilities and display functions, there has more recently come into use highly sophisticated devices which are capable of providing real time images or recorded displays with excellant detail and good resolution of desired portions of the bodily organs being examined. In a typical such device the transducer utilized with the system comprises a phased array consisting of a plurality of transducer elements arranged in a compact linear array. Each transducer element is connected to a suitable transmitter and receiver and the transmitted pulses are so phased as to steer and focus the emitted sound beam in the desired direction. Adjustable delays provided in each receiver channel enhance the reception at the desired depth and from the same direction as the transmitted sound beam. By suitably controlling the timing of the voltages applied to the transducer elements, and by controlling the adjustable delays of the separate receiver channels, the beam can be steered to any desired angle of a fan-shaped sector and focused to any desired depth. Operation of the steered array is such that a plurality of radial lines defining the fan-shaped sector are successively generated with a relatively high number of such radial lines, typically of the order of 128 such lines, being utilized in the course of generating the entire sector.
The set of such lines are generated over a short period, typically of the order of 1/30 of a second, whereby the corresponding display on the system cathode ray tube (CRT) is a high resolution substantially real time image of the body organ portions being examined. The said visualization is--in the terminology of the present art--a so-called B-mode scan, i.e., one wherein variations of the acoustical impedance of the tissue are translated into brightness variations on the CRT screen.
Details regarding the prior art signal processing techniques utilized in apparatus of the foregoing type in order to generate the mentioned fan-shaped sector image are set forth in a number of points in the prior art. Reference may usefully be had, for example, to U.S. Pat. No. 4,005,382 to William L. Beaver entitled "Signal Processor for Ultrasonic Imaging", which patent is assigned to the assignee of the present application.
Consideration of the prior art systems as above set forth will establish that the delay mechanism usually employed in order to effect steering and focusing of the received signals was based upon use of delay lines, with various types of switching mechanisms being utilized in order to enable selective switching among the said delay lines. Such an approach, while reasonably effective for the purposes of interest, nonetheless suffers from a number of important disadvantages. These include the high cost of delay lines--especially in that the time-bandwidth product pursuant to which delay lines are evaluated and to which the cost of delay lines are accordingly correlated, is a relatively high factor in systems of this type. In particular for large aperture systems required to obtain extremely high resolution these prior systems require delay lines with long delay times in consequence of which the said time-bandwidth product was necessarily quite high.
Further, in view among other things of the aforementioned fact that for large aperture systems the data must necessarily progress through a number of such delay line elements, there is a consequent requirement for a considerable number of such delay line elements, with consequent increased circuit complexity.
In accordance with the foregoing, it may be regarded as an object of the present invention to provide an ultrasonic imaging system which utilizes a digital control and memory means for both steering and focusing of the transmitter and receiver portions of this system, and which thereby eliminates use of the aforementioned delay lines and the problems incident to utilization of same.
It is a further object of the present invention to provide an ultrasonic imaging system of the indicated character wherein the same digitally controlled delay means is used for generating transmitter and receiving timing signals, thereby permitting a simpler and less costly system.
It is a further object of the present invention to provide an ultrasonic imaging system of the aforementioned character which by virtue of the digital control features thereof may be constructed with standard commercially available parts and with a great deal of flexibility in the elements, such as the memory means, which are incorporated therein.